1. Field of the Invention
The invention relates to an improved pressure-intensified fuel injection apparatus for injecting fuel into the combustion chamber of an internal combustion engine.
2. Description of the Prior Art
Both pressure-controlled and stroke-controlled fuel injection apparatuses are known for supplying fuel in direct-injection diesel engines. In common rail systems, the injection pressure can be adapted to the load and speed and a pre-injection can be used to reduce noise. As a result, the combustion process can be optimally tuned. A high injection pressure is required in order to reduce emissions and to achieve high specific outputs. The achievable pressure level of the pressure reservoir, however, is limited for strength reasons. A further pressure increase of the injection pressure is possible by using a pressure intensifier. Currently, there are known pressure intensifiers, with high intensification ratios of approx. 1:7. In these known pressure-intensified fuel injection apparatuses, the pressure intensifier is disposed in the injector and is controlled by means of a 3/2-port directional-control valve. A fuel injection apparatus of this generic type is known, for example, from EP 0 562 046 B1. In these known injection apparatuses, the pressure intensifier and all of the on/off valves are integrated into the injector, which requires a greater amount of space and results in an overall module that is very expensive to produce. The invention therefore concerns the use and design of a pressure intensifier in a common rail system to increase the injection pressure.
For better comprehension of the specification and the claims, a few terms will be explained below: the fuel injection apparatus according to the invention can be embodied both as stroke-controlled and as pressure-controlled. In the context of the invention, the term stroke-controlled fuel injection apparatus is understood to mean that a movable nozzle needle opens and closes the injection opening as a function of the hydraulic cooperation of the fuel pressures in a nozzle chamber and in a control chamber. A pressure reduction inside the control chamber produces a stroke of the nozzle needle. Alternatively, an adjusting element (actuator) can be used to displace the nozzle needle. In a pressure-controlled fuel injection apparatus according to the invention, the fuel pressure prevailing in the nozzle chamber of an injector moves the nozzle needle counter to the action of the closing force (spring) so that the injection opening is unblocked for an injection of fuel from the nozzle chamber into the cylinder. The pressure with which the fuel emerges from the nozzle chamber into a cylinder of an internal combustion engine is referred to as the injection pressure, whereas a system pressure is understood to be the pressure that prevails in the fuel inside the fuel injection apparatus or at which it is stored in the pressure reservoir. Fuel metering means supplying a definite quantity of fuel for injection. Leakage is understood to be a quantity of fuel, which is generated during operation of a fuel injection apparatus (e.g. a guidance leakage) but not used for injection, and flows into the return. The pressure level of the return can have a standing pressure.
A fuel injection apparatus according to the invention is proposed in order to reduce manufacturing costs and to increase flexibility in the installation of fuel injection apparatuses.
The use of simple modules permits a favorable series production. To that end, the pressure intensifier in a pressure-intensified fuel injection apparatus (common rail system) is constructed as an individual functional module, which can optionally be integrated into the fuel injection apparatus and can be easily installed in different locations. This permits flexible reaction to the space and installation requirements of the engine manufacturer. Installing the pressure intensifier module at the pressure reservoir, for example, permits the achievement of a very small, compact injector. The modular design permits the production of an injection system module for various engine requirements. Therefore, simpler common rail injection systems without pressure intensification for inexpensive engines (e.g. in small cars) can be comprised of the same components as more expensive, functionally expanded, pressure-intensified systems with a higher injection pressure for high-quality engines. The modular design is possible in both stroke-controlled and pressure-controlled systems.
In order to further increase flexibility, it is possible to divide the pressure intensifier and the associated on/off valves into individual modular blocks (pressure intensifier module and valve module). Then the pressure intensifier module can also be used in other injection systems, for example in a distributor pump. This also makes it possible to place the valve module at the pressure reservoir and the pressure intensifier module at the injector.
In modern injectors, it is standard to provide a lateral high pressure supply by means of an inlet connector. The inlet connector is clamped with a fastening device between the engine and the injector. The high-pressure supply line is then connected to the inlet connector.
It is particularly advantageous to combine the pressure intensifier and the on/off valve of the pressure intensifier for each cylinder into a subassembly module A, that is disposed in the cylinder head so that hydraulic connection to the injector is produced and a connection is formed for the connecting line to the pressure reservoir. Advantageously, the subassembly module A is clamped between the injector and the engine, comparable to the position of the inlet connector that is standard in modern injectors. A seal can be produced between the two modules among other ways by pressing the two modules against each other by means of the component attachment.
If the module comprised of the pressure intensifier and the on/off valve is replaced by an inlet connector, then this produces a normal common rail system without a pressure intensifier. Consequently, the functionality of the injection system can be flexibly adapted to the requirements of various ranges of engine use.
It is also particularly advantageous to combine the injector and pressure intensifier for each cylinder into a subassembly module and to embody the pressure intensifier-on/off valve as a separate subassembly module B. Advantageously, this subassembly module B is then clamped between the injector and the engine, comparable to the position of the inlet connector that is standard in modern injectors. This allows optimal use to be made of the existing space in the cylinder head.
It is also particularly advantageous to combine the injector and the pressure intensifier-on/off valve for each cylinder into a subassembly module and to embody the pressure intensifier as a separate subassembly module C. Advantageously, this subassembly module C is then clamped between the injector and the engine, comparable to the position of the inlet connector that is standard in modern injectors so that a hydraulic connection to the injector is produced and a connection is formed for the connecting line to the pressure reservoir. This allows optimal use to be made of the existing space in the cylinder head and simultaneously produces a lateral high-pressure supply, which permits a favorable connection to the pressure reservoir.
To further reduce costs and increase flexibility, a number of injectors are associated with the same pressure intensifier module and valve module. The reduced number of required pressure intensifier modules permits further reduction of the system costs. In this connection, each injector can be designed to have a minimal dead volume. Connecting a number of injectors in parallel can achieve a dead volume downstream of the pressure intensifier, which dead volume is correct for a system tuning.